Step 1

Fill a large bowl with ice and water

Step 2

Peel the potatoes and slice them lengthwise into ⅓ -inch thick sticks

Step 3

Alternatively you can use a mandolin slicer that has a ⅜ -inch setting

Step 4

Add the potatoes to the ice water and soak for 15 minutes

Step 5

Drain and pat completely dry.Attach a deep-fry thermometer to the side of a large, heavy pot

Step 6

Add the peanut oil to the pot over medium high heat

Step 7

Once the oil reaches 300°F, working in batches, carefully add the potatoes to the hot oil, and cook until beginning to soften but not browned, 3-4 minutes

Step 8

Transfer the potatoes to a paper-towel-lined sheet pan.Meanwhile, heat a large skillet over high heat

Step 9

Pat the steak dry and season all over with 2 teaspoons salt

Step 10

Add the olive oil

Step 11

Once the oil is just smoking, add the steak and cook until medium-rare (see Note) about 4-6 minutes per side

Step 12

Transfer the steak to a cutting board and top with the butter

Step 13

Let the steak rest for 5 to 10 minutes

Step 14

Increase the peanut oil temperature to 350°F

Step 15

Working in batches, return the potatoes to the hot oil and cook until golden brown and crispy, about 5 minutes

Step 16

Transfer the fries to the paper-towel-lined sheet pan

Step 17

Season with remaining ½ teaspoon salt and pepper to taste

Step 18

Thinly slice the steak against the grain

Step 19

Serve with the frites and garlic aioli on the side.